<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>  </title>
    <style>
        body{
            background-color: #f4f4f4;
            color: #444;
        }

        .box{
            width: 300px;
            height: 300px;
            background-color: blue;
        }

        .child{
            width: 100px;
            height: 100px;
            background-color: green;
        }
    </style>
</head>
<body>
    <h1>测试</h1>
    <div class="box">
        <div class="child">测试</div>
    </div>
</body>
</html>